<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>这是分支页面</title>
    <style>
        .box{
            width: 500px;
            height: 500px;
            background-color: red;
            position: relative;
        }
        .class{
            width: 200px;
            height: 200px;
            background-color: blue;
            position: absolute;
            margin: auto;
            top: 0;
            bottom: 0;
            left: 0;
            right: 0;
        }
    </style>
</head>
<body>
    <div class="box">
        <div class="class"></div>
    </div>
</body>
</html>